This invention relates to improvements in power supplies and specifically to power supplies for delivering high frequency high energy pulses.
Capacitor discharge systems are commonly employed for the delivery of high frequency energy pulses having alternate polarities. A typical application for this type of system is to supply energy to induction heating loads operating at frequencies in the kilocycle range. Such a load, commonly taking the form of a parallel resonant tank circuit, can readily be driven by high energy pulses delivered at a repetition rate equal to a sub-multiple of the natural resonant frequency of the tank circuit. However, although the repetition rate of the delivered pulses can be lower than the operating frequency of the tank circuit, the width of the pulses should not exceed one-half cycle of the resonant frequency. Thus, pulses utilized for driving tank circuits operating at 50 kilocycles, for example, must be narrow, not exceeding about 10 microseconds. Furthermore, although the repetition rate of the pulses can be lower than the operating frequency of the tank circuit, the repetition rate is nevertheless high, and the pulse generation demands the use of rapid acting, efficient switching elements.
Some prior art high frequency high power supply systems have employed energy storage capacitors which are alternately charged and then discharged through the tank circuit. In addition, saturable reactors have been employed in the capacitor discharge circuits of such systems. As those skilled in the art will appreciate, saturable reactors include a saturating ferromagnetic core and manifests its unsaturated impedance during portions of the operating cycle wherein the core is not saturated and is capable of developing a high rate of change of core flux. On the other hand, saturated impedance is manifested when the maximum flux density of the core has been reached and the core becomes substantially unable to develop any further rate of change of flux. In the saturated state, the device behaves essentially as an air core reactor, having an inductance comparable to what would prevail in the absence of the core material. The core material of such reactors must be capable of the duty imposed by frequent excursions in and out of saturation without overheating. Secondly, the device must posses a suitably low saturated inductance to discharge the capacitor into the load at the required rate.